Tidy muting code.

OpenRA.Platforms.Default/OpenAlSoundEngine.cs

@@ -207,9 +207,6 @@ namespace OpenRA.Platforms.Default
 			if (!TryGetSourceFromPool(out source))
 				return null;
 
-			if (Game.Settings.Sound.Mute)
-				Game.Sound.MuteAudio();
-
 			var slot = sourcePool[source];
 			slot.Pos = pos;
 			slot.FrameStarted = currFrame;